Method and system for gram load stabilization by repetitive mechanical back bending of a head suspension assembly

ABSTRACT

A method for stabilizing gram load of a head suspension assembly. The invention includes a mechanical back bending process. After forming, the suspension is subjected to residual stress. During mechanical back bending of the load beam, the applied stress is in the opposite direction of the forming operation. Subsequently, the resultant residual stress around the pre load area is reversed and acted against the pre-existing residual stress remaining from the forming operation. The net effect is a reduction and/or the elimination of residual stress altogether. Depending on the pre-load geometry and desired spring force, the degree of back bending is varied. Typically, a one-time back bending is not sufficient to stabilize the spring region at a microstructure level. It has been demonstrated that such repetitive back bending operation can effectively bring mobile dislocations into equilibrium, and thus reduce or eliminate the hysteresis loop.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The application claims priority of U.S. Provisional Application No 60/398,962 filed Jul. 25, 2002, commonly assigned, and in the name of Visit Thaveeprungsriporn, which is incorporated by reference for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK.

[0003] Not applicable

BACKGROUND OF THE INVENTION

[0004] The present invention relates to memory storage devices. More particularly, the invention provides an apparatus and method for stabilizing a load of the head suspension assembly of a magnetic disc drive. Preferably, the apparatus and method utilizes cyclic cold working for such stabilization by back bending a portion of the pre-loaded suspension assembly.

[0005] Head suspension assemblies have been commonly used in rigid magnetic disk drives to accurately position the read and write head in close proximity to the spinning storage medium. Such assemblies include a base plate, a load beam and a flexure (gimbal) to which a slider is to be mounted. The slider support the read/write head and possess special aerodynamic shape allowing the head to fly over the air bearing created by the rotating disk. The load beam is generally composed of an actuator mounting section, a spring and a rigid region. The spring region gives the suspension a spring force or preload counteracting the aerodynamic lift force created by the spinning medium during reading/writing. The flexure is mounted at the distal end of the load beam and support the slider allowing this one to have pitch and roll movement in order to follow the irregularities of the disk surface.

[0006] A conventional manufacturing method for such suspension is composed of steps including: etching, trace mounting, forming, stabilization, gram adjust, pitch and roll adjust, detab, cleaning, packaging, and possibly others. From a thin sheet of stainless steel, a strip of pre-shaped suspensions are formed by chemical etching. Next the trace or circuit, giving electrical connectivity to the head is mounted. Each flat strip is then fed to the gram load adjustment machine. The method forms the spring region (e.g., large bending) giving a large initial gram load. Such forming method is generally realized by stamping, rolling, or coining and results in a non-equilibrium microstructure of the spring region. A phase of stabilization of the spring region is often necessary. Generally, the use of heat treatment is employed to re-distribute the stress in stainless steel. Then the suspension's gram load is often fine adjusted, which gives the suspension its nominal preload. Such fine adjustment is mainly accomplished by mechanical bending and/or laser irradiation, which is described in U.S. Pat. No. 5,682,780. Once the gram load has been adjusted, the suspension is fed to the pitch and roll adjustment apparatus, then the suspension are separated from the strip, cleaned, and individually packed. Unfortunately, numerous limitations exist with the convention methods. As merely an example, the fine adjustment of the suspension is often difficult to perform in an accurate and efficient manner. These and other limitations are described throughout the present specification and more particularly below.

[0007] From the above, it is seen that an improved method for manufacturing disk drive apparatus is desirable.

SUMMARY OF THE INVENTION

[0008] According to the present invention, techniques related to memory storage devices are provided. More particularly, the invention provides an apparatus and method for stabilizing a load of the head suspension assembly of a magnetic disc drive. Preferably, the apparatus and method utilizes cyclic cold working for such stabilization by back bending a portion of the pre-loaded suspension assembly.

[0009] As the storage density of magnetic disks increases, the flying height of actual disks drive is quickly decreasing, making suspension gram load a desirable parameter of the suspension. This gram load need to have a reduce deviation or a minimum deviation from the target spring force during long term operation especially in high temperature and humidity environment.

[0010] Furthermore, to pre-form the spring force on the load beam, the pre-load area is mechanically bent by stamping, rolling or coining. This mechanical deformation generates non-uniform stress distribution across the load beam thickness, which needs to be properly re-distributed; otherwise, a long-term relaxation is expected causing a decrease in gram load affecting the fly height performance. The prior art practice has been to subject the stainless steel to a temperature between 250 and 350 Degrees Celsius for a period of time. The entire heat-treating process however takes much longer time to accommodate the pre-heating and cooling steps resulting in a significant loss in cycle time and productivity. Furthermore, recent models of suspension also has a trace gimbal attached to the suspension which comprises of polyimide cover layer and multi-metal layers of gold, nickel and copper, New feature such as visco-elastic damper and laminated load beam are also developed. The use of heat treatment is not a preferred choice due to concerns regarding the structural integrity of the polyimide and the possibility of copper and nickel migration. The present invention proposes a replacing stabilization method based on cyclic mechanical back bending of the spring region and describes the associated apparatus.

[0011] The present invention provide the manufacturer a way to ensure better quality gram load adjustment for a lower cost by proposing a alternative solution to the heat-based gram load stabilization.

[0012] In a specific embodiment, the invention provides a process for manufacturing a disk drive apparatus. The process includes providing a load beam in a head suspension assembly. The load beam has a spring region. The method forms a pre-load region in the spring region by causing a bend in a first direction in the spring region within the load beam. The bend includes a residual stress within a vicinity of the spring region. The method also includes releasing the residual stress in the spring region by causing a counter bend in a second direction in the spring region, whereupon the first direction is counter to the second direction.

[0013] In an alternative specific embodiment, the invention provides a method for manufacturing suspension assemblies for hard disk drives. The method includes providing a suspension including a pre-load region, which has a residual stress within a vicinity of the pre-load region. The method determines a degree of back-bending beyond z-height desired to compensate for the residual stress in the pre-load region. The method also includes performing a back bending process on the pre-load region of the suspension to release a portion of the residual stress in the pre-load region.

[0014] In an alternative specific embodiment, the invention includes a suspension assembly for hard disk drives. The suspension assembly includes a suspension member including a pre-load region; whereupon the pre-load region is free from a residual stress within a vicinity of the pre-load region.

[0015] Other and further features as well as advantages characterizing the invention will appear from the following detailed description and associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a simplified isometric view of the suspension assembly 10 according to an embodiment of the present invention.

[0017]FIG. 2 is a simplified profile view of a suspension assembly 10 according to an embodiment of the present invention.

[0018]FIG. 3 is a simplified flow diagram of the full suspension manufacturing according to an embodiment of the present invention.

[0019]FIG. 4 is a simplified flow diagram of the gram load adjustment process according to an embodiment of the present invention.

[0020]FIG. 5 is a simplified comparison of the gram load loss over 100 cycles between a heat treated suspension and a non heat treated suspension according to an embodiment of the present invention.

[0021]FIG. 6 is a simplified comparison of the gram load loss over 100,000 cycles between a heat-treated, a non heat-treated and a back bended suspension according to an embodiment of the present invention.

[0022]FIGS. 7 and 8 are more detailed isometric views of back bending stabilization station 601 according to an embodiment of the present invention.

[0023]FIG. 9 is a more detailed side view of the clamping apparatus 640 according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] According to the present invention, techniques related to memory storage devices are provided. More particularly, the invention provides an apparatus and method for stabilizing a load of the head suspension assembly of a magnetic disc drive. Preferably, the apparatus and method utilizes cyclic cold working for such stabilization by back bending a portion of the pre-loaded suspension assembly.

[0025]FIG. 1 is a simplified isometric view of the suspension assembly 10 according to an embodiment of the present invention. FIG. 2 is a simplified profile view of a suspension assembly 10 according to an embodiment of the present invention. These diagrams are merely illustrations, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many other variations, modifications, and alternatives. As shown, a head suspension assembly (HSA) 10 is formed with a flexure 11, an air bearing slider 12 mounted on the flexure 11, a load beam 13, a base plate 14, among other elements. The load beam 13 has a mounting region 15 on its proximal end and a flexure mounting region 17 on its distal end. The base plate 14 is typically welded on the mounting region 15 and ensures rigidity of the mounting. The load beam comprises also a spring region 16 between its proximal and distal region. The spring region 16 gives the suspension the ability to maintain, a precise distance between the head and the media to be read (fly height) by giving the beam a pre load force counteracting the air bearing created by the spinning medium. This preload is called gram load of the suspension. Further details of manufacturing the suspension are provided throughout the present specification and more particularly below.

[0026]FIG. 3 shows a simplified flow diagram of the suspension manufacturing. This diagram is merely an illustration, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many other variations, modifications, and alternatives. From a thin sheet of stainless steel, the general shapes of the suspension are etched by photochemical etching 100. Then different stamping operations 200 are carried out (reinforcement shapes, dimple and load/unload tab formation). Next is the welding assembly of the base plate, load beam and gimbal 300. To enable the reading and writing function of the head, a flexible polyamide and copper electric circuit (trace) is attached to the head 400. At this stage the suspension is given an initial pre load by rolling or coining forming 500. Once pre formed the suspension gram load is fine adjusted 600. The last operations are pitch and roll adjustment 700, detab (separation) 800, cleaning and packing 900. The gram load adjustment process is provided in more detail below.

[0027]FIG. 4 gives a detailed flow diagram of the gram load adjust machine with its four stations. This diagram is merely an illustration, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many other variations, modifications, and alternatives. After forming the suspension is first presented to the stabilization station 601. At this stage the suspension is cyclically back bended in order for the residual stress present in the spring region 16 and due to the forming to be redistributed and/or relieved. Details are given throughout the present specification but more particularly in a later section. Once stabilized the suspension gram load is measured on the station 602. This station can be any conventional or specific known apparatus for gram load measurement. This initial measurement is used to determine the parameter of the gram load adjustment station 603 (bending angle for cold working adjustment and/or irradiation time for laser adjustment). Once adjusted to its nominal gram load the suspension is fed to the last gram load measurement station 604 which valid or reject the suspension.

[0028] As a part of customer specifications for gram load reliability test, suspensions must generally exhibit a low change in gram-load during usage. FIG. 5 shows a comparison of gram load change over 100 cycles between heat-treated and non heat-treated suspension. The heat-treated parts demonstrate almost no change in gram-load while the no-heat treated parts experience a slight loss in gram-load. The loss is most pronounced during the first 20 cycles and stabilized afterwards.

[0029]FIG. 5 also demonstrates that a stabilization (heat treatment in this case) is necessary to avoid gram load loss during usage. The disclosed invention proposes a new stabilization process. A cyclic back bending of the suspension load beam is proposed in replacement to the costly and time-consuming heat treatment stabilization.

[0030]FIG. 6 gives a comparison of the gram load loss over 100,000 cycles for a non-stabilized, a heat-treated and a back bended suspension (5 times back bending). After improving and/or optimizing the algorithm and amount of deflection during cyclic cold working, it has been shown that there is no noticeable difference between the heat-treated parts and cyclically cold-worked parts. Several reliability tests including gram-load change versus z-height adjusts, gram-load distribution, thermal shock test, and resonance performance shown that cyclic back bending can efficiently replace heat treatment stabilization.

[0031]FIGS. 7 and 8 are detailed isometric views of the mechanical stabilization station 601. The embodiments of the stabilization station 601 include a walking beam 610, a clamping device 640 and a back bending apparatus 670. The walking beam 610 (not completely represented) index feed the suspensions to the station 601. This device can be any known walking index feeder.

[0032] The clamping device 640 is composed of an upper clamp 641, a linear actuator 643 and a plurality of clamping pins 642. The upper clamp 641 is mounted on the linear actuator 643 through to the holder 644. The upper clamp 641 had a plurality of holes 647 (FIG. 9) positioned in alignment with the plurality of clamping pins 642. The linear actuator 643 is used for lowering and raising the upper clamp 641 during clamping and unclamping operations. The linear actuator 643 is attached to the station base (not represented) thanks to the holder 625. The plurality of clamping pins 642 is attached to the linear actuator 671 through the holders 645 and 646. The plurality of clamping pins 642 is mounted on springs 648 in order to allow the pins 646 to retract when touching the base plate 14 as well as maintain the clamping force during back bending operation. Details of this device are given on FIG. 9.

[0033] The bending apparatus 670 includes a linear actuator 671, a holder 672 and a bending arm 673. The bending arm 673 is attached to the moving part of the actuator 671 through the holder 672. The bending arm is composed of a roll 678 having a length equivalent to five suspensions width and a roll holder 674. The linear actuator 671 is used for raising and lowering the bending arm during back bending. The linear actuator 671 is attached to the station base (not represented) by to the holder 675 and 676.

[0034] The holder 676 and 625 as well as the walking beam 610 are mounted on a common base not shown on FIG. 7 and 8.

[0035] The multiple back bending operation is composed of several steps. First, the walking beam 610 presents the suspensions to be stabilized into the clamping assembly. After the base plate has been aligned with the plurality a pins 642 and the upper clamp 641 by the walking beam 610, the upper clamp 641 is driven to close position shown of FIG. 9b. The actuator 671 is driven to simultaneously raise the plurality of pins 642 and the bending roll 678. The plurality of pins 642 clamp the base plate 14 of the fives suspension to be back bended. At the same time the bending roll 678 applies a bending force on the suspension load beam 13 in an opposite direction than the forming operation. The roll 678 is kept in high position during a short time then lowered while the suspensions 10 are released from the clamping system 640. Once the operation terminated the walking beam 610 move the strips 20 of one suspension and the cycle start again.

[0036] The clamping and bending apparatus respectively 640 and 670 are designed to clamp and back bend five suspension at the same time. The feeding being incremental, one suspension will be back bended five times. Indeed a one time back bending is not sufficient to stabilize the gram load at a microstructure level. Experiments have proven that five is the optimum number of back bending needed for best stabilization according to a specific embodiment.

[0037] One of ordinary skill in the art would recognize many other variations, modifications, and alternatives. The above example is merely an illustration, which should not unduly limit the scope of the claims herein. It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. 

What is claimed is:
 1. A process for manufacturing a disk drive apparatus, the process comprising: providing a load beam in a head suspension assembly, the load beam having a spring region; forming a pre-load region in the spring region by causing a bend in a first direction in the spring region within the load beam, the bend including a residual stress within a vicinity of the spring region; and redistributing the residual stress in the spring region by causing a counter bend in a second direction in the spring region, whereupon the first direction is counter to the second direction.
 2. The process of claim 1 wherein the redistributing is provided by at least one counter bend in the second direction; wherein the forming of the pre-load region mechanically bends the spring region in the first direction.
 3. A method for manufacturing suspension assemblies for hard disk drives, the method comprising: providing a suspension including a pre-load region, the pre-load region including a residual stress within a vicinity of the pre-load region; determining a degree of back-bending beyond z-height desired to compensate for the residual stress in the pre-load region; and performing a back bending process on the pre-load region of the suspension to release a portion of the residual stress in the pre-load region.
 4. The method claim in 3 wherein the back bending process is provided more than one time.
 5. A suspension assembly for hard disk drives, the suspension assembly comprising: a suspension member including a pre-load region; whereupon the pre-load region is free from a residual stress within a vicinity of the pre-load region.
 6. The assembly of claim 5 wherein the residual stress is caused by manufacturing the pre-load region.
 7. The assembly of claim 5 wherein the pre-load region comprises a bent region in a first direction.
 8. The assembly of claim 7 wherein the pre-load comprises a re-bend region, the re-bend region being counter to the bend region.
 9. A process for manufacturing a disk drive apparatus, the process comprising: providing a load beam in a head suspension assembly, the load beam having a spring region; forming a pre-load region in the spring region by causing a bend in a first direction in the spring region within the load beam, the bend including a residual stress within a vicinity of the spring region; and redistributing and/or relieving the residual stress in the spring region by causing a counter bend in a second direction in the spring region, whereupon the first direction is counter to the second direction.
 10. The process of claim 1 wherein the redistributing and/or relieving is provided by at least one counter bend in the second direction; wherein the forming of the pre-load region mechanically bends the spring region in the first direction. 